Tech: repairing Vectrex monitor

[jasonbar]

Howdy-

I'm working on a Vectrex w/ no image. Overall, it's in good condition & clean, with no obvious signs of damage.

It plays blind. I hear the Minestorm sounds & hear sounds of another game if I insert a game cartridge. I hear deflection chatter that corresponds to the game graphics (Vectrex splash screen, Minestorm title, demo gameplay start), so I *think* that the logic PCB & deflection circuit are OK.


The monitor neck board was a little askew when I opened the Vectrex, so I straightened it. No change.

What I've tried so far:
1 - Brightness knob.
2 - Reflowed solder on both ends of neck board wires, deflection cable pin headers on power PCB, AC wires powering power PCB, brightness knob pot, around the flyback cage, & a few other places.
3 - Reseated & cleaned chips/sockets on logic PCB. (I know, a long shot...)
4 - Cleaned & reflowed solder & biased pins/sockets on 4-wire DC power connector on logic PCB that feeds to power PCB, to ensure good connections.
5 - Poked here & there w/ a plastic tool to see if I could get an image to pop up by flexing a PCB & closing a cracked solder joint.
6 - Checked resistance on brightness pot. Seems to respond OK.
7 - Confirmed a secure connection of the flyback wire to the CRT, under the suction cup.


Then, I dug into troubleshooting manual & went through the "No Vector" section in order (skipping some items):
a) +/-5V & -13V at connector J204.
YUP!
b) AC input to voltage to power supply PCB at EP105-EP106 & EP105-EP104 should be 8.6VAC.
I'M GETTING AROUND 10.8-11.V VAC. PROBLEM? TOO HIGH? NEED A NEW TRANSFORMER?
c) Check that there are no shorts between power supply & GND (T503 (in) - T401 (in)).
THIS MIGHT BE MY PROBLEM. EACH OF THESE TRANSFORMERS HAS +IN, -IN, +OUT, -OUT. I'M NOT SURE WHICH OF THE 2 INS I SHOULD BE CHECKING. OR SHOULD I CHECK BOTH INS ON EACH TRANSFORMER? ON T401, ONE OF THE INS IS SHORTED TO GROUND & THE OTHER ISN'T. ON T503, BOTH INS SEEM TO BE SHORTED TO GROUND & TO ONE OF THE OUTS--LOOKS AS IF T503 IS SUSPECT. I SHOULD REMOVE IT & CHECK IT & CHECK FOR SHORTS ON ITS 4 PADS TO GROUND, AGREED?
d) Check for short b/t heat sink & IC401 heat sink.
GETTING THE BIG HEAT SINK OFF IS A BEAR, BUT I CAN USE A FLASHLIGHT & SEE A GAP B/T IC 401 & THE BIG HEAT SINK, SO I THINK THIS IS OK.
e) Check supply voltage at CRT PCB pins 2, 3, 5, 6 (+40, +.3mV, -29 to +3 brightness, & +135).
I'M NOT SURE WHERE THESE ARE. I PROBED THE 5 PIGTAILED WIRES GOING INTO THE NECK BOARD & DIDN'T GET MUCH IN THE WAY OF READINGS--ARE THESE DC OR AC?

Thanks,
-Jason

[kokovec]

I've repaired a few Vextri and it's never the same problem twice.
The first thing I always do is a cap replacement. This takes allot of time and it's a challenge to avoid lifting the traces but it has fixed most of my issues. Sometimes blowing some "freeze-all" on caps around the board will point out a faulty one.
It could still be on the logic board. The mux might have given up the ghost or the op-amps.
If you're poking around the power board it goes without say that caution is required. Especially if you're measuring voltage while the Vectrex is live.
I have yet to come across a bad transformer but I wouldn't rule it out. Usually when they die they short out so if you're seeing voltage it may be OK.

[jasonbar]

Thanks. Yah, I just did a cap kit the other day. A challenge for me. But, it's probably easier than chasing down a problem. My fear is that I'll do a fabulous cap kit job & then it still won't work. =O

Thanks,
-Jason

[kokovec]

I can't stress enough that the tube should be safely discharged before replacing the caps.
My suggestion is to replace the easily accessible caps first and try out the Vectrex before replacing the rest.
The zero reference pot typically needs to be tweaked after a cap replacement but you'll need an oscilloscope for that. If you're lucky you won't need to do it.

[jasonbar]

Thanks--I'm familiar w/ discharging the tube, but it's always good to bring that up.

Which pot is the zero reference pot?

Thanks,
-Jason

[kokovec]

R302. Procedure can be found on page 12 of the service manual.

[jasonbar]

R302, in my layman's terms is just the "center the image diagonally" pot that's readily accessible after removing the console back cover.

I'm not sure why an oscilloscope is required when adjusting this pot. I can pop on an overlay like the Minestorm overlay & use its grid to eyeball when the image is centered.

Thanks,
-Jason

[kokovec]

R302 is used to fine tune the D/A output's op-amp that feeds the MUX (for Y and Z axis) as well as directly drive the X axis and comparator used for reading the analog joystick.
Centering the screen is done by adjusting the ring magnets on the yoke.

[jasonbar]

Thanks for the scoop!

[braqoon]

HI, I know this post is old but did you got your Vectrex working ? Got exact same issue and did pretty much what you did but still no luck. I'm trying to avoid re-cap job as mine looks fine. I got Jamicon caps in mine and all seems to be in a good shape. Those i checked are perfectly fine.

Do you got any update on this ?

Thanks

[jasonbar]

Hi braqoon.

I'm sorry, but I can hardly remember what happened 3 days ago, let alone 3 years ago...

My bad for not following up to my own thread.

If I had to guess, I guess that I'd guess that the cap kit fixed it...I guess...?

Good luck,
-Jason

[braqoon]

Thanks for update.